The invention is based on a fuel injection device for internal combustion engines. In a fuel injection device of this kind, which has been disclosed by DE 196 24 001 A1, the fuel injection valve member, which is supplied by a high-pressure fuel source, is controlled by means of various hydraulic forces that act on the fuel injection valve member opening and closing direction. The fuel injection valve member has an injection valve member for controlling an injection opening and, at an end remote from the injection opening, encloses a control chamber, which is supplied with high fuel pressure from a high-pressure fuel source by means of a throttled supply conduit. The control chamber can be relieved of pressure by means of the control valve that is actuated by a piezoelectric actuator so that in this instance, by means of the hydraulic pressure acting on the pressure shoulder of the injection valve member and with the lack of hydraulic high-pressure in the control chamber, the injection valve member is opened. In contrast, when the control chamber is closed, the high fuel pressure is built up again in the control chamber and the injection valve member is brought back into the closed position. In the known fuel injection device, the control valve is disposed in an outlet conduit of the control chamber. In addition to the connection from the high-pressure reservoir to the control chamber, in the known fuel injection device, another connection to the pressure chamber must be produced. The chamber is defined by the pressure shoulder of the injection valve member and is continuously kept at a high pressure. This known device is costly for the reason described since in addition to the multiple connection from the high-pressure fuel source to the control chamber and to the pressure chamber, the inlet and outlet cross sections to the control chamber and the pressure-impinged surfaces on the injection valve member must also be matched to one another exactly.
The fuel injection device has an advantage that through the use of simple means, the injection valve member of the fuel injection valve can be rapidly and precisely opened by the piezoelectric drive mechanism for a preinjection and is then closed again in order to be subsequently opened for the ensuing main injection. In this connection, it is significantly advantageous that the control valve member only has to be moved back and forth once for the entire procedure. In particular, with continuous equiaxial movement of the control valve member, the short phase of the opening of both valve seats in the control valve permits the achievement of very short high-pressure supply times in order to produce a preinjection.
In a particularly advantageous manner despite smaller working strokes of a piezoelectric actuator, large opening strokes of the control valve member can be achieved by means of a hydraulic transmission. Another advantageous embodiment of the invention is comprised in that, the high fuel pressure, which comes from the high-pressure fuel source and prevails against the control valve member when the control valve member is closed, produces a force compensation on the control valve member since equivalent surfaces are the same size in both movement directions of the control valve member. According to the inventor, the surface area ratio of surfaces subjected to the pressure acting on the control valve member is selected so that the high pressure of the high-pressure fuel source prevailing in the recess loads the control valve member slightly more in the opening direction than in the closing direction. The closing takes place as a result of restoring spring forces on the control valve member.
Finally in a last embodiment, the pressure impingement of he control valve member is selected so that the inlet of the pressure line to the valve chamber takes place coaxial to the valve tappet so that when the valve head is resting against a second valve seat, the connection from the high-pressure fuel source to the valve chamber or to the pressure chamber of the fuel injection valve is closed. In this connection, the control valve member is in fact acted on by relatively high opening forces, but the valve tappet bore is only acted on by low-pressure fuel so that the leakage losses of the control valve are low. The pressure impingement on the valve tappet or the valve tappet bore that guides the valve tappet takes place only during the connection of the pressure line to the pressure chamber, i.e. during the injection phase of the fuel injection device.